This application is related to commonly owned copending application xe2x80x9cHigh Average Power Fiber Laser System With Phase Conjugationxe2x80x9d, having inventor H. Komine, Ser. No. 09/132,168, filed on Aug. 11, 1998; xe2x80x9cHigh Average Power Solid State Laser With Phase Front Controlxe2x80x9d, having inventor H. Komine, Ser. No. 09/066,063, filed on Apr. 24, 1998; xe2x80x9cHigh Average Power Fiber Laser System With Phase Front Controlxe2x80x9d, having inventor H. Komine, Ser. No. 09/132,178, filed on Aug. 11, 1998, and;
xe2x80x9cA Dynamic Optical Micrometerxe2x80x9d, Ser. No. 09/283,484, now U.S. Pat. No. 6,243,168, having inventors Donald Heflinger and Lee Heflinger, xe2x80x9cA Dynamic Optical Phase State Detectorxe2x80x9d, Ser. No. 09/289,946,now U.S. Pat. No. 6,147,755, having inventors Donald Heflinger and Lee Heflinger, and xe2x80x9cHeterodyne Wavefront Sensorxe2x80x9d, Ser. No. 09/283,604, now U.S. Pat. No. 6,229,616, having inventors Stephen Brosnan, Donald Heflinger and Lee Heflinger, filed concurrently with this patent application.
1. Field of the Invention
The present invention generally relates to a high-average-power fiber laser system, and more particularly such a system that includes a high speed parallel wavefront.
2. Description of the Prior Art
High power laser weapon systems are generally known in the art. An example of such a high power laser system is disclosed in commonly owned U.S. Pat. No. 5,198,607. Such laser weapon systems normally include a high power laser weapon and a tracking system for locking the high power laser on a target, such as a ballistic missile, cruise missile, bomber or the like. Such laser weapons are used to destroy or xe2x80x9ckillxe2x80x9d such targets.
Such laser weapon systems are known to employ relatively large chemical lasers. However, such chemical lasers have several drawbacks. For example, such chemical lasers are relatively bulky and require special fuels that create logistic difficulties for field deployment. As such, a need has developed to provide relatively efficient compact laser weapons that can operate from electrical generators. Unfortunately, the power output level of known fiber laser systems, which are relatively compact and efficient is heretofore been insufficient for use in laser weapon systems. Such fiber lasers are known to include a dual-clad optical fiber. More particularly, the optical fiber includes a core, for example formed from SiO2 and doped with a rare earth ion, such as, Yb or Nd, Er or other rare earth ions. The doped core is clad by two different cladding layers having different indices of refraction to cause the total internal reflection of the light within the optic fiber to form a single mode fiber. Examples of such optical fibers used for fiber laser are disclosed in U.S. Pat. Nos. 4,815,079; 5,087,108; 5,218,665; 5,291,501; 5,461,692; 5,530,709; and 5,566,196. Such fiber lasers are known to be diode pumped and generate relatively low average power levels, for example, up to 35 watts at a light-to-light efficiency of about 70 %. Unfortunately, such relatively low power levels of fiber lasers have made them unsuitable for many applications including defense applications.
Various attempts have been to increase the average power output of such fiber lasers. Examples of such attempts are disclosed in U.S. Pat. Nos. 5,121,460 and 5,373,576. Such attempts generally involve the use of relatively complex optical fibers. For example, the ""460 patent teaches the use of an optical fiber having a neodymium doped primary core surrounded by a first elliptically shaped multi-mode cladding of fused silica. A samarium doped secondary core is formed around the primary core within the first layer of cladding. The secondary core is utilized for suppressing higher order modes.
The ""576 patent also discloses the use of a relatively high average power optical fiber. More particularly, the ""576 patent discloses an optical fiber formed, with a doped core surrounded by a first multi-mode cladding layer formed from, for example, fused silica. A second cladding layer is formed around the first cladding layer and formed from a cross-link polymeric material having a liquid component. The optical fibers disclosed in the ""460 and ""576 patents are relatively complex. Thus, there is a need for a relatively high average power fiber laser that utilizes relatively less complex optical fibers than known systems.
The limitations in obtaining high optional powers from a single optical fiber has directed attention to using an array of low power optical fibers that are coherently coupled so as to deliver a well collimated high average power beam with a controlled phase front. To control the phase front of this high power beam, the optical phase in each individual emitting fiber in the array needs to be sampled and actively controlled. Current art for performing this phase front detection is provided by existing wavefront sensors. However, the existing wavefront sensors operate in ways that limit their application to detecting and actively controlling the phase front of a high average power optical fiber array.
Current art is limited by the speed of the camera used in the wavefront sensor that measures the two-dimensional state-of-phase of the output beam. Such cameras are usually read out serially, which imposes a bottleneck in the phase measurement speed. Another limitation involves an ambiguity in the phase measurement that uses an interferometer. The ambiguity can only be resolved by the addition of more components, storing intermediate data, and making computations with that data. The computation bottleneck is a serious limitation to the phase measurement throughput.
What is needed, therefore, is a high speed wavefront sensor to sample the wavefront and actively control the state of phase of each individual optical fiber in a high average power fiber laser array.
Briefly, the present invention relates to an improved relatively high average power fiber laser system with a high-speed, parallel wavefront sensor.